The dopamine hypothesis of schizophrenia states that symptoms may be caused by an excess of dopamine in the mid-brain and a reduction in dopamine in the prefrontal cortex. This hypothesis came from the finding that drugs that block dopamine (dopamine antagonists, such as antipsychotics) reduce the positive symptoms of schziphrenia. Additionally, drugs used to treat Parkinson's disease (that increase dopamine, such as L-DOPA) can have the side effect of producing psychosis-like symptoms.
This hypothesis has been supported not only by drug therapies but through post-mortem and brain imaging studies that report excess D2 receptors in the brains of people with schizophrenia.However, the relationship between dopamine and schizophrenia is merely correlational therefore we cannot determine causality, it is over simplistic as we know other neurotransmitters such as serotonin play a role and this is not considered and therefore this hypothesis may be criticised as being reductionist. Despite this it has useful applications and is perhaps one of the oldest and most widely supported hypothesis of schizophrenia.
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